The Lebanon-based Islamic militant group Hezbollah has been ferrying trained and combat-ready mercenaries from Eastern Europe into Syria, The Daily Star reports, citing security sources.

The first batch of paid soldiers from Eastern Europe arrived last January into Lebanon's Beirut-Rafic Hariri International Airport, before being whisked away to the border with Syria by Hezbollah vans.

The sources confirmed that these Eastern European fighters wear Hezbollah military uniforms as well as yellow bands on their heads to show their loyalty. The sources also revealed that Eastern European company M Security Group, one of the most prominent organizations of its kind in the region, recruited the fighters specifically to send them to Syria to fight alongside the Syrian regime for a large monthly salary as well as insurance for their families.

Currently, more than 5,000 Europeans are estimated to be fighting in Syria, prompting concern among leaders in Europe. Many fear these fighters may return radicalized and ready to wage war within the boundaries of Europe.